In 1867, Ezra Decoto, a local landowner sold land to the railroad. A settlement grew up around the place. A post office operated in Decoto from 1871 to 1959, with a closure from 1872 to 1875.
Decoto is shown on historical maps  which show it north of Alameda Creek and in the flat land below the hills, on the railroad tracks. This corresponds to present day Union City.
Decoto Road in Union City exists in the present day and the intersection of Decoto Road and Mission Blvd. in Union City appears to be approximately where the town or village of Decoto was located.
The Decoto area's population is largely Latino, mostly Mexican. Starting in the 1930s and especially during World War 2 Mexican families began moving to Decoto. Many were braceros that came to work during the labor shortages during the War years. Decoto's population is still predominantly Latino.
During the early 1970s the Chicano Movement was in full swing and racial tensions were high in Decoto between the Latino community and police and the local Union City Government. In April 1974 Alberto Terrones was shot and killed during a robbery by Union City police. Riots erupted in Decoto. To calm tensions, Union City Police Chief William Cann came to speak at Our lady of Rosary Catholic Church in Decoto. He was shot by a sniper and died a few months later. 
United Airlines Flight 615 crashed near Decoto in 1951.
- Durham, David L. (1998). California's Geographic Names: A Gazetteer of Historic and Modern Names of the State. Quill Driver Books. p. 623. ISBN 9781884995149.
- Historical Map collection: Farm Ownership Map 004, Eden, Wasington, Decoto, Rancho Arroyo de la Alameda
- Assassination in Decoto Timothy Swenson
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